In recent years, a hybrid car, a fuel cell car, an electric car, and the like which run with driving force from a motor have attracted attention as one of measures for addressing environmental issues. Such a vehicle is equipped with a power storage device, and a state of charge of a power storage device should accurately be estimated in order to sufficiently exhibit performance of the power storage device.
In view of such issues, for example, Japanese Patent Laying-Open No. 2005-331482 discloses a state of charge operation device for accurately finding a state of charge while continuing operation of a state of charge with minimum necessary accuracy even though data cannot normally be obtained, to thereby suppress influence on a control system to the minimum. This state of charge operation device includes first operation means for operating a first state of charge based on a sum value of charging and discharging currents of a power storage device, second operation means for operating a second state of charge based on an open-circuit voltage estimated from internal impedance of the power storage device, third operation means for operating a state of charge of the power storage device by weighting and combining the first state of charge and the second state of charge by using a weight set in accordance with a state of use of the power storage device, first abnormal condition processing means for stopping operation by the second operation means and fixing a weight value such that the combined value in the third operation means is set to the first state of charge when voltage data of the power storage device cannot normally be obtained, second abnormal condition processing means for stopping operation by the first operation means and fixing a weight value such that the combined value in the third operation means is set to the second state of charge when current data of the power storage device cannot normally be obtained, and third abnormal condition processing means for estimating, when temperature data of the power storage device cannot normally be obtained, a temperature from the calculated internal impedance based on a voltage of the power storage device and the charging and discharging currents and adopting this estimated temperature as an operation parameter in the first operation means and the second operation means.
According to the state of charge operation device disclosed in the literature described above, a state of charge can accurately be found by making use of both advantages of a state of charge based on a sum of currents and a state of charge based on an open-circuit voltage, and in addition, even though an abnormal condition occurs in any system for measuring a voltage, a current, and a temperature and data cannot normally be obtained, operation of a state of charge can be continued with minimum necessary accuracy and influence on a control system can be suppressed to the minimum.